/*
 * jquant1.c
 *
 * Copyright (C) 1991-1995, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains 1-pass color quantization (color mapping) routines.
 * These routines provide mapping to a fixed color map using equally spaced
 * color values.  Optional Floyd-Steinberg or ordered dithering is available.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"

#ifdef QUANT_1PASS_SUPPORTED


/*
 * The main purpose of 1-pass quantization is to provide a fast, if not very
 * high quality, colormapped output capability.  A 2-pass quantizer usually
 * gives better visual quality; however, for quantized grayscale output this
 * quantizer is perfectly adequate.  Dithering is highly recommended with this
 * quantizer, though you can turn it off if you really want to.
 *
 * In 1-pass quantization the colormap must be chosen in advance of seeing the
 * image.  We use a map consisting of all combinations of Ncolors[i] color
 * values for the i'th component.  The Ncolors[] values are chosen so that
 * their product, the total number of colors, is no more than that requested.
 * (In most cases, the product will be somewhat less.)
 *
 * Since the colormap is orthogonal, the representative value for each color
 * component can be determined without considering the other components;
 * then these indexes can be combined into a colormap index by a standard
 * N-dimensional-array-subscript calculation.  Most of the arithmetic involved
 * can be precalculated and stored in the lookup table colorindex[].
 * colorindex[i][j] maps pixel value j in component i to the nearest
 * representative value (grid plane) for that component; this index is
 * multiplied by the array stride for component i, so that the
 * index of the colormap entry closest to a given pixel value is just
 *    sum( colorindex[component-number][pixel-component-value] )
 * Aside from being fast, this scheme allows for variable spacing between
 * representative values with no additional lookup cost.
 *
 * If gamma correction has been applied in color conversion, it might be wise
 * to adjust the color grid spacing so that the representative colors are
 * equidistant in linear space.  At this writing, gamma correction is not
 * implemented by jdcolor, so nothing is done here.
 */


/* Declarations for ordered dithering.
 *
 * We use a standard 16x16 ordered dither array.  The basic concept of ordered
 * dithering is described in many references, for instance Dale Schumacher's
 * chapter II.2 of Graphics Gems II (James Arvo, ed. Academic Press, 1991).
 * In place of Schumacher's comparisons against a "threshold" value, we add a
 * "dither" value to the input pixel and then round the result to the nearest
 * output value.  The dither value is equivalent to (0.5 - threshold) times
 * the distance between output values.  For ordered dithering, we assume that
 * the output colors are equally spaced; if not, results will probably be
 * worse, since the dither may be too much or too little at a given point.
 *
 * The normal calculation would be to form pixel value + dither, range-limit
 * this to 0..MAXJSAMPLE, and then index into the colorindex table as usual.
 * We can skip the separate range-limiting step by extending the colorindex
 * table in both directions.
 */

#define ODITHER_SIZE  16    /* dimension of dither matrix */
/* NB: if ODITHER_SIZE is not a power of 2, ODITHER_MASK uses will break */
#define ODITHER_CELLS ( ODITHER_SIZE * ODITHER_SIZE )   /* # cells in matrix */
#define ODITHER_MASK  ( ODITHER_SIZE - 1 ) /* mask for wrapping around counters */

typedef int ODITHER_MATRIX[ODITHER_SIZE][ODITHER_SIZE];
typedef int ( *ODITHER_MATRIX_PTR )[ODITHER_SIZE];

static const UINT8 base_dither_matrix[ODITHER_SIZE][ODITHER_SIZE] = {
    /* Bayer's order-4 dither array.  Generated by the code given in
     * Stephen Hawley's article "Ordered Dithering" in Graphics Gems I.
     * The values in this array must range from 0 to ODITHER_CELLS-1.
     */
    {   0, 192, 48, 240, 12, 204, 60, 252,  3, 195, 51, 243, 15, 207, 63, 255 },
    { 128, 64, 176, 112, 140, 76, 188, 124, 131, 67, 179, 115, 143, 79, 191, 127 },
    {  32, 224, 16, 208, 44, 236, 28, 220, 35, 227, 19, 211, 47, 239, 31, 223 },
    { 160, 96, 144, 80, 172, 108, 156, 92, 163, 99, 147, 83, 175, 111, 159, 95 },
    {   8, 200, 56, 248,  4, 196, 52, 244, 11, 203, 59, 251,  7, 199, 55, 247 },
    { 136, 72, 184, 120, 132, 68, 180, 116, 139, 75, 187, 123, 135, 71, 183, 119 },
    {  40, 232, 24, 216, 36, 228, 20, 212, 43, 235, 27, 219, 39, 231, 23, 215 },
    { 168, 104, 152, 88, 164, 100, 148, 84, 171, 107, 155, 91, 167, 103, 151, 87 },
    {   2, 194, 50, 242, 14, 206, 62, 254,  1, 193, 49, 241, 13, 205, 61, 253 },
    { 130, 66, 178, 114, 142, 78, 190, 126, 129, 65, 177, 113, 141, 77, 189, 125 },
    {  34, 226, 18, 210, 46, 238, 30, 222, 33, 225, 17, 209, 45, 237, 29, 221 },
    { 162, 98, 146, 82, 174, 110, 158, 94, 161, 97, 145, 81, 173, 109, 157, 93 },
    {  10, 202, 58, 250,  6, 198, 54, 246,  9, 201, 57, 249,  5, 197, 53, 245 },
    { 138, 74, 186, 122, 134, 70, 182, 118, 137, 73, 185, 121, 133, 69, 181, 117 },
    {  42, 234, 26, 218, 38, 230, 22, 214, 41, 233, 25, 217, 37, 229, 21, 213 },
    { 170, 106, 154, 90, 166, 102, 150, 86, 169, 105, 153, 89, 165, 101, 149, 85 }
};


/* Declarations for Floyd-Steinberg dithering.
 *
 * Errors are accumulated into the array fserrors[], at a resolution of
 * 1/16th of a pixel count.  The error at a given pixel is propagated
 * to its not-yet-processed neighbors using the standard F-S fractions,
 *		...	(here)	7/16
 *		3/16	5/16	1/16
 * We work left-to-right on even rows, right-to-left on odd rows.
 *
 * We can get away with a single array (holding one row's worth of errors)
 * by using it to store the current row's errors at pixel columns not yet
 * processed, but the next row's errors at columns already processed.  We
 * need only a few extra variables to hold the errors immediately around the
 * current column.  (If we are lucky, those variables are in registers, but
 * even if not, they're probably cheaper to access than array elements are.)
 *
 * The fserrors[] array is indexed [component#][position].
 * We provide (#columns + 2) entries per component; the extra entry at each
 * end saves us from special-casing the first and last pixels.
 *
 * Note: on a wide image, we might not have enough room in a PC's near data
 * segment to hold the error array; so it is allocated with alloc_large.
 */

#if BITS_IN_JSAMPLE == 8
typedef INT16 FSERROR;      /* 16 bits should be enough */
typedef int LOCFSERROR;     /* use 'int' for calculation temps */
#else
typedef INT32 FSERROR;      /* may need more than 16 bits */
typedef INT32 LOCFSERROR;   /* be sure calculation temps are big enough */
#endif

typedef FSERROR FAR * FSERRPTR;  /* pointer to error array (in FAR storage!) */


/* Private subobject */

#define MAX_Q_COMPS 4       /* max components I can handle */

typedef struct {
    struct jpeg_color_quantizer pub;/* public fields */

    /* Initially allocated colormap is saved here */
    JSAMPARRAY sv_colormap; /* The color map as a 2-D pixel array */
    int        sv_actual; /* number of entries in use */

    JSAMPARRAY colorindex;  /* Precomputed mapping for speed */
    /* colorindex[i][j] = index of color closest to pixel value j in component i,
     * premultiplied as described above.  Since colormap indexes must fit into
     * JSAMPLEs, the entries of this array will too.
     */
    boolean is_padded;      /* is the colorindex padded for odither? */

    int Ncolors[MAX_Q_COMPS];/* # of values alloced to each component */

    /* Variables for ordered dithering */
    int                row_index; /* cur row's vertical index in dither matrix */
    ODITHER_MATRIX_PTR odither[MAX_Q_COMPS];/* one dither array per component */

    /* Variables for Floyd-Steinberg dithering */
    FSERRPTR fserrors[MAX_Q_COMPS];/* accumulated errors */
    boolean  on_odd_row;    /* flag to remember which row we are on */
} my_cquantizer;

typedef my_cquantizer * my_cquantize_ptr;


/*
 * Policy-making subroutines for create_colormap and create_colorindex.
 * These routines determine the colormap to be used.  The rest of the module
 * only assumes that the colormap is orthogonal.
 *
 *  * select_ncolors decides how to divvy up the available colors
 *    among the components.
 *  * output_value defines the set of representative values for a component.
 *  * largest_input_value defines the mapping from input values to
 *    representative values for a component.
 * Note that the latter two routines may impose different policies for
 * different components, though this is not currently done.
 */


LOCAL int
select_ncolors( j_decompress_ptr cinfo, int Ncolors[] ) {
/* Determine allocation of desired colors to components, */
/* and fill in Ncolors[] array to indicate choice. */
/* Return value is total number of colors (product of Ncolors[] values). */
    int nc = cinfo->out_color_components;/* number of color components */
    int max_colors = cinfo->desired_number_of_colors;
    int total_colors, iroot, i, j;
    boolean changed;
    long temp;
    static const int RGB_order[3] = { RGB_GREEN, RGB_RED, RGB_BLUE };

    /* We can allocate at least the nc'th root of max_colors per component. */
    /* Compute floor(nc'th root of max_colors). */
    iroot = 1;
    do {
        iroot++;
        temp = iroot;   /* set temp = iroot ** nc */
        for ( i = 1; i < nc; i++ ) {
            temp *= iroot;
        }
    } while ( temp <= (long) max_colors );/* repeat till iroot exceeds root */
    iroot--;        /* now iroot = floor(root) */

    /* Must have at least 2 color values per component */
    if ( iroot < 2 ) {
        ERREXIT1( cinfo, JERR_QUANT_FEW_COLORS, (int) temp );
    }

    /* Initialize to iroot color values for each component */
    total_colors = 1;
    for ( i = 0; i < nc; i++ ) {
        Ncolors[i] = iroot;
        total_colors *= iroot;
    }
    /* We may be able to increment the count for one or more components without
     * exceeding max_colors, though we know not all can be incremented.
     * Sometimes, the first component can be incremented more than once!
     * (Example: for 16 colors, we start at 2*2*2, go to 3*2*2, then 4*2*2.)
     * In RGB colorspace, try to increment G first, then R, then B.
     */
    do {
        changed = FALSE;
        for ( i = 0; i < nc; i++ ) {
            j = ( cinfo->out_color_space == JCS_RGB ? RGB_order[i] : i );
            /* calculate new total_colors if Ncolors[j] is incremented */
            temp = total_colors / Ncolors[j];
            temp *= Ncolors[j] + 1;/* done in long arith to avoid oflo */
            if ( temp > (long) max_colors ) {
                break;
            }       /* won't fit, done with this pass */
            Ncolors[j]++; /* OK, apply the increment */
            total_colors = (int) temp;
            changed = TRUE;
        }
    } while ( changed );

    return total_colors;
}


LOCAL int
output_value( j_decompress_ptr cinfo, int ci, int j, int maxj ) {
/* Return j'th output value, where j will range from 0 to maxj */
/* The output values must fall in 0..MAXJSAMPLE in increasing order */
/* We always provide values 0 and MAXJSAMPLE for each component;
 * any additional values are equally spaced between these limits.
 * (Forcing the upper and lower values to the limits ensures that
 * dithering can't produce a color outside the selected gamut.)
 */
    return (int) ( ( (INT32) j * MAXJSAMPLE + maxj / 2 ) / maxj );
}


LOCAL int
largest_input_value( j_decompress_ptr cinfo, int ci, int j, int maxj ) {
/* Return largest input value that should map to j'th output value */
/* Must have largest(j=0) >= 0, and largest(j=maxj) >= MAXJSAMPLE */
/* Breakpoints are halfway between values returned by output_value */
    return (int) ( ( (INT32) ( 2 * j + 1 ) * MAXJSAMPLE + maxj ) / ( 2 * maxj ) );
}


/*
 * Create the colormap.
 */

LOCAL void
create_colormap( j_decompress_ptr cinfo ) {
    my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
    JSAMPARRAY colormap;    /* Created colormap */
    int total_colors;   /* Number of distinct output colors */
    int i, j, k, nci, blksize, blkdist, ptr, val;

    /* Select number of colors for each component */
    total_colors = select_ncolors( cinfo, cquantize->Ncolors );

    /* Report selected color counts */
    if ( cinfo->out_color_components == 3 ) {
        TRACEMS4( cinfo, 1, JTRC_QUANT_3_NCOLORS,
                  total_colors, cquantize->Ncolors[0],
                  cquantize->Ncolors[1], cquantize->Ncolors[2] );
    } else {
        TRACEMS1( cinfo, 1, JTRC_QUANT_NCOLORS, total_colors );
    }

    /* Allocate and fill in the colormap. */
    /* The colors are ordered in the map in standard row-major order, */
    /* i.e. rightmost (highest-indexed) color changes most rapidly. */

    colormap = ( *cinfo->mem->alloc_sarray )
               ( (j_common_ptr) cinfo, JPOOL_IMAGE,
                (JDIMENSION) total_colors, (JDIMENSION) cinfo->out_color_components );

    /* blksize is number of adjacent repeated entries for a component */
    /* blkdist is distance between groups of identical entries for a component */
    blkdist = total_colors;

    for ( i = 0; i < cinfo->out_color_components; i++ ) {
        /* fill in colormap entries for i'th color component */
        nci = cquantize->Ncolors[i];/* # of distinct values for this color */
        blksize = blkdist / nci;
        for ( j = 0; j < nci; j++ ) {
            /* Compute j'th output value (out of nci) for component */
            val = output_value( cinfo, i, j, nci - 1 );
            /* Fill in all colormap entries that have this value of this component */
            for ( ptr = j * blksize; ptr < total_colors; ptr += blkdist ) {
                /* fill in blksize entries beginning at ptr */
                for ( k = 0; k < blksize; k++ ) {
                    colormap[i][ptr + k] = (JSAMPLE) val;
                }
            }
        }
        blkdist = blksize;  /* blksize of this color is blkdist of next */
    }

    /* Save the colormap in private storage,
     * where it will survive color quantization mode changes.
     */
    cquantize->sv_colormap = colormap;
    cquantize->sv_actual = total_colors;
}


/*
 * Create the color index table.
 */

LOCAL void
create_colorindex( j_decompress_ptr cinfo ) {
    my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
    JSAMPROW indexptr;
    int i, j, k, nci, blksize, val, pad;

    /* For ordered dither, we pad the color index tables by MAXJSAMPLE in
     * each direction (input index values can be -MAXJSAMPLE .. 2*MAXJSAMPLE).
     * This is not necessary in the other dithering modes.  However, we
     * flag whether it was done in case user changes dithering mode.
     */
    if ( cinfo->dither_mode == JDITHER_ORDERED ) {
        pad = MAXJSAMPLE * 2;
        cquantize->is_padded = TRUE;
    } else {
        pad = 0;
        cquantize->is_padded = FALSE;
    }

    cquantize->colorindex = ( *cinfo->mem->alloc_sarray )
                            ( (j_common_ptr) cinfo, JPOOL_IMAGE,
                             (JDIMENSION) ( MAXJSAMPLE + 1 + pad ),
                             (JDIMENSION) cinfo->out_color_components );

    /* blksize is number of adjacent repeated entries for a component */
    blksize = cquantize->sv_actual;

    for ( i = 0; i < cinfo->out_color_components; i++ ) {
        /* fill in colorindex entries for i'th color component */
        nci = cquantize->Ncolors[i];/* # of distinct values for this color */
        blksize = blksize / nci;

        /* adjust colorindex pointers to provide padding at negative indexes. */
        if ( pad ) {
            cquantize->colorindex[i] += MAXJSAMPLE;
        }

        /* in loop, val = index of current output value, */
        /* and k = largest j that maps to current val */
        indexptr = cquantize->colorindex[i];
        val = 0;
        k = largest_input_value( cinfo, i, 0, nci - 1 );
        for ( j = 0; j <= MAXJSAMPLE; j++ ) {
            while ( j > k ) {/* advance val if past boundary */
                k = largest_input_value( cinfo, i, ++val, nci - 1 );
            }
            /* premultiply so that no multiplication needed in main processing */
            indexptr[j] = (JSAMPLE) ( val * blksize );
        }
        /* Pad at both ends if necessary */
        if ( pad ) {
            for ( j = 1; j <= MAXJSAMPLE; j++ ) {
                indexptr[-j] = indexptr[0];
                indexptr[MAXJSAMPLE + j] = indexptr[MAXJSAMPLE];
            }
        }
    }
}


/*
 * Create an ordered-dither array for a component having ncolors
 * distinct output values.
 */

LOCAL ODITHER_MATRIX_PTR
make_odither_array( j_decompress_ptr cinfo, int ncolors ) {
    ODITHER_MATRIX_PTR odither;
    int j, k;
    INT32 num, den;

    odither = (ODITHER_MATRIX_PTR)
              ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE,
                                           SIZEOF( ODITHER_MATRIX ) );
    /* The inter-value distance for this color is MAXJSAMPLE/(ncolors-1).
     * Hence the dither value for the matrix cell with fill order f
     * (f=0..N-1) should be (N-1-2*f)/(2*N) * MAXJSAMPLE/(ncolors-1).
     * On 16-bit-int machine, be careful to avoid overflow.
     */
    den = 2 * ODITHER_CELLS * ( (INT32) ( ncolors - 1 ) );
    for ( j = 0; j < ODITHER_SIZE; j++ ) {
        for ( k = 0; k < ODITHER_SIZE; k++ ) {
            num = ( (INT32) ( ODITHER_CELLS - 1 - 2 * ( (int)base_dither_matrix[j][k] ) ) )
                  * MAXJSAMPLE;
            /* Ensure round towards zero despite C's lack of consistency
             * about rounding negative values in integer division...
             */
            odither[j][k] = (int) ( num < 0 ? -( ( -num ) / den ) : num / den );
        }
    }
    return odither;
}


/*
 * Create the ordered-dither tables.
 * Components having the same number of representative colors may
 * share a dither table.
 */

LOCAL void
create_odither_tables( j_decompress_ptr cinfo ) {
    my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
    ODITHER_MATRIX_PTR odither;
    int i, j, nci;

    for ( i = 0; i < cinfo->out_color_components; i++ ) {
        nci = cquantize->Ncolors[i];/* # of distinct values for this color */
        odither = NULL; /* search for matching prior component */
        for ( j = 0; j < i; j++ ) {
            if ( nci == cquantize->Ncolors[j] ) {
                odither = cquantize->odither[j];
                break;
            }
        }
        if ( odither == NULL ) {/* need a new table? */
            odither = make_odither_array( cinfo, nci );
        }
        cquantize->odither[i] = odither;
    }
}


/*
 * Map some rows of pixels to the output colormapped representation.
 */

METHODDEF void
color_quantize( j_decompress_ptr cinfo, JSAMPARRAY input_buf,
                JSAMPARRAY output_buf, int num_rows ) {
/* General case, no dithering */
    my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
    JSAMPARRAY colorindex = cquantize->colorindex;
    register int pixcode, ci;
    register JSAMPROW ptrin, ptrout;
    int row;
    JDIMENSION col;
    JDIMENSION width = cinfo->output_width;
    register int nc = cinfo->out_color_components;

    for ( row = 0; row < num_rows; row++ ) {
        ptrin = input_buf[row];
        ptrout = output_buf[row];
        for ( col = width; col > 0; col-- ) {
            pixcode = 0;
            for ( ci = 0; ci < nc; ci++ ) {
                pixcode += GETJSAMPLE( colorindex[ci][GETJSAMPLE( *ptrin++ )] );
            }
            *ptrout++ = (JSAMPLE) pixcode;
        }
    }
}


METHODDEF void
color_quantize3( j_decompress_ptr cinfo, JSAMPARRAY input_buf,
                 JSAMPARRAY output_buf, int num_rows ) {
/* Fast path for out_color_components==3, no dithering */
    my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
    register int pixcode;
    register JSAMPROW ptrin, ptrout;
    JSAMPROW colorindex0 = cquantize->colorindex[0];
    JSAMPROW colorindex1 = cquantize->colorindex[1];
    JSAMPROW colorindex2 = cquantize->colorindex[2];
    int row;
    JDIMENSION col;
    JDIMENSION width = cinfo->output_width;

    for ( row = 0; row < num_rows; row++ ) {
        ptrin = input_buf[row];
        ptrout = output_buf[row];
        for ( col = width; col > 0; col-- ) {
            pixcode  = GETJSAMPLE( colorindex0[GETJSAMPLE( *ptrin++ )] );
            pixcode += GETJSAMPLE( colorindex1[GETJSAMPLE( *ptrin++ )] );
            pixcode += GETJSAMPLE( colorindex2[GETJSAMPLE( *ptrin++ )] );
            *ptrout++ = (JSAMPLE) pixcode;
        }
    }
}


METHODDEF void
quantize_ord_dither( j_decompress_ptr cinfo, JSAMPARRAY input_buf,
                     JSAMPARRAY output_buf, int num_rows ) {
/* General case, with ordered dithering */
    my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
    register JSAMPROW input_ptr;
    register JSAMPROW output_ptr;
    JSAMPROW colorindex_ci;
    int * dither;       /* points to active row of dither matrix */
    int row_index, col_index;/* current indexes into dither matrix */
    int nc = cinfo->out_color_components;
    int ci;
    int row;
    JDIMENSION col;
    JDIMENSION width = cinfo->output_width;

    for ( row = 0; row < num_rows; row++ ) {
        /* Initialize output values to 0 so can process components separately */
        jzero_far( (void FAR *) output_buf[row],
                  (size_t) ( width * SIZEOF( JSAMPLE ) ) );
        row_index = cquantize->row_index;
        for ( ci = 0; ci < nc; ci++ ) {
            input_ptr = input_buf[row] + ci;
            output_ptr = output_buf[row];
            colorindex_ci = cquantize->colorindex[ci];
            dither = cquantize->odither[ci][row_index];
            col_index = 0;

            for ( col = width; col > 0; col-- ) {
                /* Form pixel value + dither, range-limit to 0..MAXJSAMPLE,
                 * select output value, accumulate into output code for this pixel.
                 * Range-limiting need not be done explicitly, as we have extended
                 * the colorindex table to produce the right answers for out-of-range
                 * inputs.  The maximum dither is +- MAXJSAMPLE; this sets the
                 * required amount of padding.
                 */
                *output_ptr += colorindex_ci[GETJSAMPLE( *input_ptr ) + dither[col_index]];
                input_ptr += nc;
                output_ptr++;
                col_index = ( col_index + 1 ) & ODITHER_MASK;
            }
        }
        /* Advance row index for next row */
        row_index = ( row_index + 1 ) & ODITHER_MASK;
        cquantize->row_index = row_index;
    }
}


METHODDEF void
quantize3_ord_dither( j_decompress_ptr cinfo, JSAMPARRAY input_buf,
                      JSAMPARRAY output_buf, int num_rows ) {
/* Fast path for out_color_components==3, with ordered dithering */
    my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
    register int pixcode;
    register JSAMPROW input_ptr;
    register JSAMPROW output_ptr;
    JSAMPROW colorindex0 = cquantize->colorindex[0];
    JSAMPROW colorindex1 = cquantize->colorindex[1];
    JSAMPROW colorindex2 = cquantize->colorindex[2];
    int * dither0;      /* points to active row of dither matrix */
    int * dither1;
    int * dither2;
    int row_index, col_index;/* current indexes into dither matrix */
    int row;
    JDIMENSION col;
    JDIMENSION width = cinfo->output_width;

    for ( row = 0; row < num_rows; row++ ) {
        row_index = cquantize->row_index;
        input_ptr = input_buf[row];
        output_ptr = output_buf[row];
        dither0 = cquantize->odither[0][row_index];
        dither1 = cquantize->odither[1][row_index];
        dither2 = cquantize->odither[2][row_index];
        col_index = 0;

        for ( col = width; col > 0; col-- ) {
            pixcode  = GETJSAMPLE( colorindex0[GETJSAMPLE( *input_ptr++ ) +
                                               dither0[col_index]] );
            pixcode += GETJSAMPLE( colorindex1[GETJSAMPLE( *input_ptr++ ) +
                                               dither1[col_index]] );
            pixcode += GETJSAMPLE( colorindex2[GETJSAMPLE( *input_ptr++ ) +
                                               dither2[col_index]] );
            *output_ptr++ = (JSAMPLE) pixcode;
            col_index = ( col_index + 1 ) & ODITHER_MASK;
        }
        row_index = ( row_index + 1 ) & ODITHER_MASK;
        cquantize->row_index = row_index;
    }
}


METHODDEF void
quantize_fs_dither( j_decompress_ptr cinfo, JSAMPARRAY input_buf,
                    JSAMPARRAY output_buf, int num_rows ) {
/* General case, with Floyd-Steinberg dithering */
    my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
    register LOCFSERROR cur;/* current error or pixel value */
    LOCFSERROR belowerr;    /* error for pixel below cur */
    LOCFSERROR bpreverr;    /* error for below/prev col */
    LOCFSERROR bnexterr;    /* error for below/next col */
    LOCFSERROR delta;
    register FSERRPTR errorptr; /* => fserrors[] at column before current */
    register JSAMPROW input_ptr;
    register JSAMPROW output_ptr;
    JSAMPROW colorindex_ci;
    JSAMPROW colormap_ci;
    int pixcode;
    int nc = cinfo->out_color_components;
    int dir;        /* 1 for left-to-right, -1 for right-to-left */
    int dirnc;          /* dir * nc */
    int ci;
    int row;
    JDIMENSION col;
    JDIMENSION width = cinfo->output_width;
    JSAMPLE * range_limit = cinfo->sample_range_limit;
    SHIFT_TEMPS

    for ( row = 0; row < num_rows; row++ ) {
        /* Initialize output values to 0 so can process components separately */
        jzero_far( (void FAR *) output_buf[row],
                  (size_t) ( width * SIZEOF( JSAMPLE ) ) );
        for ( ci = 0; ci < nc; ci++ ) {
            input_ptr = input_buf[row] + ci;
            output_ptr = output_buf[row];
            if ( cquantize->on_odd_row ) {
                /* work right to left in this row */
                input_ptr += ( width - 1 ) * nc;/* so point to rightmost pixel */
                output_ptr += width - 1;
                dir = -1;
                dirnc = -nc;
                errorptr = cquantize->fserrors[ci] + ( width + 1 );/* => entry after last column */
            } else {
                /* work left to right in this row */
                dir = 1;
                dirnc = nc;
                errorptr = cquantize->fserrors[ci];/* => entry before first column */
            }
            colorindex_ci = cquantize->colorindex[ci];
            colormap_ci = cquantize->sv_colormap[ci];
            /* Preset error values: no error propagated to first pixel from left */
            cur = 0;
            /* and no error propagated to row below yet */
            belowerr = bpreverr = 0;

            for ( col = width; col > 0; col-- ) {
                /* cur holds the error propagated from the previous pixel on the
                 * current line.  Add the error propagated from the previous line
                 * to form the complete error correction term for this pixel, and
                 * round the error term (which is expressed * 16) to an integer.
                 * RIGHT_SHIFT rounds towards minus infinity, so adding 8 is correct
                 * for either sign of the error value.
                 * Note: errorptr points to *previous* column's array entry.
                 */
                cur = RIGHT_SHIFT( cur + errorptr[dir] + 8, 4 );
                /* Form pixel value + error, and range-limit to 0..MAXJSAMPLE.
                 * The maximum error is +- MAXJSAMPLE; this sets the required size
                 * of the range_limit array.
                 */
                cur += GETJSAMPLE( *input_ptr );
                cur = GETJSAMPLE( range_limit[cur] );
                /* Select output value, accumulate into output code for this pixel */
                pixcode = GETJSAMPLE( colorindex_ci[cur] );
                *output_ptr += (JSAMPLE) pixcode;
                /* Compute actual representation error at this pixel */
                /* Note: we can do this even though we don't have the final */
                /* pixel code, because the colormap is orthogonal. */
                cur -= GETJSAMPLE( colormap_ci[pixcode] );
                /* Compute error fractions to be propagated to adjacent pixels.
                 * Add these into the running sums, and simultaneously shift the
                 * next-line error sums left by 1 column.
                 */
                bnexterr = cur;
                delta = cur * 2;
                cur += delta;/* form error * 3 */
                errorptr[0] = (FSERROR) ( bpreverr + cur );
                cur += delta;/* form error * 5 */
                bpreverr = belowerr + cur;
                belowerr = bnexterr;
                cur += delta;/* form error * 7 */
                /* At this point cur contains the 7/16 error value to be propagated
                 * to the next pixel on the current line, and all the errors for the
                 * next line have been shifted over. We are therefore ready to move on.
                 */
                input_ptr += dirnc;/* advance input ptr to next column */
                output_ptr += dir;/* advance output ptr to next column */
                errorptr += dir;/* advance errorptr to current column */
            }
            /* Post-loop cleanup: we must unload the final error value into the
             * final fserrors[] entry.  Note we need not unload belowerr because
             * it is for the dummy column before or after the actual array.
             */
            errorptr[0] = (FSERROR) bpreverr;/* unload prev err into array */
        }
        cquantize->on_odd_row = ( cquantize->on_odd_row ? FALSE : TRUE );
    }
}


/*
 * Allocate workspace for Floyd-Steinberg errors.
 */

LOCAL void
alloc_fs_workspace( j_decompress_ptr cinfo ) {
    my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
    size_t arraysize;
    int i;

    arraysize = (size_t) ( ( cinfo->output_width + 2 ) * SIZEOF( FSERROR ) );
    for ( i = 0; i < cinfo->out_color_components; i++ ) {
        cquantize->fserrors[i] = (FSERRPTR)
                                 ( *cinfo->mem->alloc_large )( (j_common_ptr) cinfo, JPOOL_IMAGE, arraysize );
    }
}


/*
 * Initialize for one-pass color quantization.
 */

METHODDEF void
start_pass_1_quant( j_decompress_ptr cinfo, boolean is_pre_scan ) {
    my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
    size_t arraysize;
    int i;

    /* Install my colormap. */
    cinfo->colormap = cquantize->sv_colormap;
    cinfo->actual_number_of_colors = cquantize->sv_actual;

    /* Initialize for desired dithering mode. */
    switch ( cinfo->dither_mode ) {
        case JDITHER_NONE:
            if ( cinfo->out_color_components == 3 ) {
                cquantize->pub.color_quantize = color_quantize3;
            } else {
                cquantize->pub.color_quantize = color_quantize;
            }
            break;
        case JDITHER_ORDERED:
            if ( cinfo->out_color_components == 3 ) {
                cquantize->pub.color_quantize = quantize3_ord_dither;
            } else {
                cquantize->pub.color_quantize = quantize_ord_dither;
            }
            cquantize->row_index = 0;/* initialize state for ordered dither */
            /* If user changed to ordered dither from another mode,
             * we must recreate the color index table with padding.
             * This will cost extra space, but probably isn't very likely.
             */
            if ( !cquantize->is_padded ) {
                create_colorindex( cinfo );
            }
            /* Create ordered-dither tables if we didn't already. */
            if ( cquantize->odither[0] == NULL ) {
                create_odither_tables( cinfo );
            }
            break;
        case JDITHER_FS:
            cquantize->pub.color_quantize = quantize_fs_dither;
            cquantize->on_odd_row = FALSE;/* initialize state for F-S dither */
            /* Allocate Floyd-Steinberg workspace if didn't already. */
            if ( cquantize->fserrors[0] == NULL ) {
                alloc_fs_workspace( cinfo );
            }
            /* Initialize the propagated errors to zero. */
            arraysize = (size_t) ( ( cinfo->output_width + 2 ) * SIZEOF( FSERROR ) );
            for ( i = 0; i < cinfo->out_color_components; i++ ) {
                jzero_far( (void FAR *) cquantize->fserrors[i], arraysize );
            }
            break;
        default:
            ERREXIT( cinfo, JERR_NOT_COMPILED );
            break;
    }
}


/*
 * Finish up at the end of the pass.
 */

METHODDEF void
finish_pass_1_quant( j_decompress_ptr cinfo ) {
    /* no work in 1-pass case */
}


/*
 * Switch to a new external colormap between output passes.
 * Shouldn't get to this module!
 */

METHODDEF void
new_color_map_1_quant( j_decompress_ptr cinfo ) {
    ERREXIT( cinfo, JERR_MODE_CHANGE );
}


/*
 * Module initialization routine for 1-pass color quantization.
 */

GLOBAL void
jinit_1pass_quantizer( j_decompress_ptr cinfo ) {
    my_cquantize_ptr cquantize;

    cquantize = (my_cquantize_ptr)
                ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE,
                                             SIZEOF( my_cquantizer ) );
    cinfo->cquantize = (struct jpeg_color_quantizer *) cquantize;
    cquantize->pub.start_pass = start_pass_1_quant;
    cquantize->pub.finish_pass = finish_pass_1_quant;
    cquantize->pub.new_color_map = new_color_map_1_quant;
    cquantize->fserrors[0] = NULL;/* Flag FS workspace not allocated */
    cquantize->odither[0] = NULL;/* Also flag odither arrays not allocated */

    /* Make sure my internal arrays won't overflow */
    if ( cinfo->out_color_components > MAX_Q_COMPS ) {
        ERREXIT1( cinfo, JERR_QUANT_COMPONENTS, MAX_Q_COMPS );
    }
    /* Make sure colormap indexes can be represented by JSAMPLEs */
    if ( cinfo->desired_number_of_colors > ( MAXJSAMPLE + 1 ) ) {
        ERREXIT1( cinfo, JERR_QUANT_MANY_COLORS, MAXJSAMPLE + 1 );
    }

    /* Create the colormap and color index table. */
    create_colormap( cinfo );
    create_colorindex( cinfo );

    /* Allocate Floyd-Steinberg workspace now if requested.
     * We do this now since it is FAR storage and may affect the memory
     * manager's space calculations.  If the user changes to FS dither
     * mode in a later pass, we will allocate the space then, and will
     * possibly overrun the max_memory_to_use setting.
     */
    if ( cinfo->dither_mode == JDITHER_FS ) {
        alloc_fs_workspace( cinfo );
    }
}

#endif /* QUANT_1PASS_SUPPORTED */
